1. Unlock Cammy, Fei Long, Dan, Sakura, Rose, and Gen.
2. Pick a character you have already used to beat Arcade Mode.
3. Win all your matches without continuing and without losing any rounds before fighting with Seth.
4. You need to get at least one "perfect" win in a round, and more than one depending on how many rounds per match you are playing.  

• 1 round match: 1 perfect round or more
• 3 round match: 2 perfect rounds or more
• 5 round match: 3 perfect rounds or more
• 7 round match: 4 perfect rounds or more
• This includes the last battle against Seth

1. Complete Arcade Mode playing as Akuma and watch (not necessary to watch everything) an ending.
2. Then, unlock Gouken as an opponent, and defeat him.

• Play using a character you're beaten the game with
  
• Do not lose a match and continue
  
• Don't even lose around. So just go with one round matches
• Achieve certain number (or more) of "Perfect" rounds.  The number of Perfect Wins you need to achieve are:If you play on
• If you play on 1 round match: 1 time or more
• If you play on 3 round match: 2 times or more
• If you play on 5 round match: 3 times or more
• If you play on 7 round match: 4 times or more
• Achieve a certain number (or more) of Super Combo -OR- Ultra Combo Finishes.  Super and Ultra finishes both count toward this number. The number of super/ultra finishes you need to achieve are:
• 1 round match: 3 times or more
• 3 round match: 5 times or more
• 5 round match: 7 times or more
• 7 round match: 9 times or more
• Achieve certain number (or more) of First Attack (this means you must score the first strike in a match--the screen gives you the "First Attack" message, and you can mostly do this without even noticing):
  

• Shoryuuken! Street FIghter IV sells 2 million copies worldwide

Via Capcom Unity